US-based X-energy has submitted an application to enter the UK Generic Design Assessment (GDA) process for its Xe-100 high temperature gas-cooled reactor (HTGR). The GDA is a voluntary, non-mandatory process offering a regulatory pathway for licensing new nuclear technologies, evaluating safety, security, safeguards, and environmental impact independent of site-specific considerations. The process was opened to advanced nuclear technologies, including small modular reactor (SMRs) in 2021.
It is administered by Office for Nuclear Regulation (ONR), Environment Agency (EA), Natural Resources Wales and the Department for Energy Security & Net Zero (DESNZ). Completion of the three-step GDA culminates in the issue of a Design Acceptance Confirmation from ONR and a Statement of Design Acceptability from EA.
The Xe-100 is an 80 MWe HTGR that can be deployed in modular 4-unit or 12-unit configurations. The design simultaneously generates grid electricity and high-temperature heat/steam. This makes it ideal for heavy industrial decarbonisation. It uses X-energy’s TRISO-X Tri-structural Isotropic particle fuel pebbles. The inert helium coolant does not become radioactive, which reduces the required physical safety perimeter.
In 2024, X-energy was selected for DESNZ’s Future Nuclear Enabling Fund to develop UK-specific deployment plans including assessment of domestic manufacturing opportunities, supply chain development, constructability, modularization studies, and fuel management. This culminated in multiple technical and commercial studies estimating a minimum of £40bn ($53.7bn) in lifetime economic value, with £12bn arising from the first project alone.
In September 2025, X-energy and Centrica signed a Joint Development Agreement for the UK’s first advanced nuclear fleet, targeting 6 GWe nationwide with Hartlepool identified as the preferred first site for a 12-unit/960 MWe Xe-100 plant. The site is adjacent to Hartlepool’s existing NPP, which is scheduled for closure in 2028. The project is currently advancing through the UK Government’s Advanced Nuclear Pipeline assessment.
X-energy began talks with UK regulatory authorities in 2024 through the Early Engagement process. The formal GDA submission builds on extensive US licensing progress and is expected to benefit from expanded collaboration between ONR and the US Nuclear Regulatory Commission (NRC) that allows direct transfer of design documentation and safety analyses. GDA applicants can leverage NRC-approved technical documents throughout the assessment, enhancing efficiency in the UK’s licensing process.
“Advanced Modular Reactors like the Xe-100 are the cornerstone of Britain’s future energy security, and would bring clean, reliable power as well as renewed opportunities for British industry,” said Alistair Black, Vice President and UK Market Lead at X-energy. “We welcome the Regulators’ recent steps towards a more efficient GDA process, and look forward to working collaboratively to support an efficient, thorough review. GDA submission marks an important milestone in bringing our technology to the UK on a fleet-scale, with the potential to create thousands of high-quality jobs where needs are greatest.”
In the US, X-energy has achieved several regulatory milestones with NRC, positioning its Xe-100 reactor and TRISO-X fuel as leaders in advanced commercial nuclear deployment. In February, X-energy’s subsidiary, TRISO-X, secured a Special Nuclear Material Licence from NRC – the first new NRC-licensed commercial fuel facility in over 50 years and the first ever authorised to handle High-assay low-enriched uranium (HALEU). The 40-year licence, approved three months ahead of schedule, allows the commercial manufacturing of up to 700,000 TRISO fuel pebbles annually at its TX-1 facility in Oak Ridge, Tennessee.
In May, NRC completed its Environmental Assessment (EA) for Dow and X-energy’s Construction Permit Application (CPA) for their proposed advanced nuclear project in Seadrift, Texas. The NRC review was completed ahead of schedule following a comprehensive independent analysis, marking a major step forward for the $2.4bn Seadrift advanced nuclear project. NRC issued a Finding of No Significant Impact (FONSI) following the EA rather than demanding a traditional, years-long Environmental Impact Statement.
Before filing for physical construction permits, X-energy systematically de-risked its reactor architecture through NRC’s topical report process. NRC formally approved X-energy’s “Transient and Safety Analysis Methodologies” Licensing Topical Report. final safety evaluation officially validated X-energy’s core computer models and safety simulation frameworks. It allows these pre-approved methodologies to be directly referenced in current and future plant applications, avoiding repetitive regulatory reviews.
The approvals directly support a multi-gigawatt pipeline, including the project with Dow in Texas and a massive 5 GWe deployment initiative with Amazon and Energy Northwest slated for 2039.
